Hi, i've bought a few of the premium investigator figures from the FFG website over the last year (I use them for Elder Sign) but I don't have 1st Ed MoM. I'd like to be able to use these investigators in MoM2Ed as well.

Any chance the app/scenarios could also include a section for selecting these figures instead of assuming we have the whole of the 1st Ed.

It is highly unlikely FFG will ever have that option in the app. What you can do however is just select 2nd edition investigators in the app, but use the 1st edition investigators on the board, and just keep track of which investigator matches up to which in the app, so if one is mentioned by name in the app you'll know who it actually effects on the board. A little finicky, but gives you the ability to use just the investigators without worry of 1st edition monsters or tiles showing up.

^ This. We did exactly this and it worked great, gives you access to another 15 investigators (which is a lot at the start, but after a few play throughs its fun to explore the new guys and gals).

I find that the investigator minis are not overly detailed either, at least face/hair wise, so you can find one that is just close enough without even noticing a big difference.